1. Field of the Invention
The present invention relates to a crossbar switch for transferring, between nodes, data that is exchanged mutually by a plurality of nodes.
2. Description of the Related Art
As described in, for example, JP 2004-102607 A, a crossbar switch is provided inside an information processor including a plurality of processor nodes and a plurality of I/O nodes, and has plural ports to connect to the processor nodes and to the I/O nodes. The crossbar switch dynamically selects and connects a desired port input section and a desired port output section to each other, enabling data transfer between the process or node and the I/O node. A mediation circuit determines the port input section and the port output section to be connected to each other.
The crossbar switch transfers data on a packet basis, so the mediation circuit performs mediation between ports on a packet basis. A packet is made of one or more flits. A flit is fixed-width data which is transferred at one cycle. If a minimum packet made of one flit is transferred, the crossbar switch has to perform mediation for each cycle in order to process the data with the throughput being maintained. In this kind of crossbar switches, a mediation result signal outputted from the mediation circuit is required for control of both the port input section and the port output section.
As an example, the crossbar switch has a configuration in which the mediation circuit is disposed in each port output section. This configuration requires a path used for transmitting a mediation request signal outputted from the port input section to the mediation circuit disposed in the port output section, and a path used for transmitting a mediation result signal outputted from the mediation circuit to the port input section. Further, the signals have to be transmitted through the paths within one cycle. The configuration, in which the crossbar switch is implemented in one LSI, includes a portion where the distance between the port input section and the port output section is long, causing a problem in that a high-frequency operation is difficult to perform.
If a register for storing the signals is provided at the middle in order to shorten the paths, used for transmitting the signals between the port input section and the port output section within one cycle, the path length for one cycle is shortened. In this case, however, a delay is caused by a cycle of storing a signal in the register and of reading the signal therefrom. This makes the mediation for each cycle difficult and causes a problem of a decreased data throughput.
Even in the other configurations, there is a possibility that it is hard to perform the high-frequency operation or to maintain the throughput, depending on the path length between the mediation circuit and the port input section and port output section.